The lighting industry has undergone a fundamental change by developing the white LED. Huge energy savings are possibly by means of the LED light and this industry makes a positive contribution to the energy transition.
In addition to the energy saving effects, the LED also makes possible completely new luminaire designs. In particular the possibility of feeding light by means of a so-called LED strip laterally into a transparent plate creates the precondition of designing very flat luminaires. Here, it is also desired to have the greatest possible, preferably complete, transparency of the luminaire in order to realize a “light, floating” design.
A problem of this type of luminaire is that the light which is fed from the LED via the edge into the plate and then guided in the plate has to be deflected by about 90° in order for it to exit the plate surface perpendicularly to illuminate the floor or ceiling of the room to be lighted. The solution according to the prior art ensures that a surface of the plate and/or the light exit surface of the plate is provided with a surface structuring. As a result, it is possible to produce reflections and light refraction in the area of the substrate-air interface.
According to a solution approach, e.g. pyramid-shaped or conical recesses are realized in the surface by mechanical methods. However, the drawback is that such structured plates are no longer sufficiently transparent.
DE 10 2004 026 585 B4 discloses a light distributor having a light-distributing structure consisting of microstructures and macrostructures. This is again a surface structuring which in the described case is produced by means of laser structuring. This is understood to mean a local and precise removal of material on the surface. This method is used for transparent melting plastic materials, such as PMMA (polymethyl methacrylate, commercial name: Plexiglas or Perspex, acrylic glass). In this method, the plastic material is heated, material evaporates and depolymerizes. Due to the sudden heat exposure, individual particles are explosively removed from the material in adjoining areas, at other locations the material just melts and solidifies again. Although this type of surface structuring can be controlled in relatively precise fashion, the problem of the no longer perfectly transparent surface continues to exist.
The irradiation of various substrates, in particular also of plastic materials and glasses, is presently scrutinized in basic research and without concrete reference to the light distributor and luminaire design topics. It is already known that the refractive index of a substrate can be changed locally in the case of the specific irradiation with laser pulses. For this purpose, short-term pulse lasers are used, in particular lasers within the femtosecond range. For a successful local change in the refractive index it is necessary to synchronize pulse parameters, on the one hand, and the treated material, on the other hand. An example of such a scientific investigation relating to refractive index changes in PMMA is e.g. the publication by Alexandra Baum et al.: “NUV and NIR Femtosecond Laser Modification of PMMA”, Proceedings of LPM 2007—The 8th International Symposium on Laser Precision Micro fabrication. 
DE 10 2009 025 072 A1 discloses a method for producing a region with increased refractive index. The method comprises providing a substrate from polycarbonate and producing the region in the substrate by irradiation. This region with increased refractive index can form an optical waveguide. In addition to polycarbonate as a substrate, the use of PMMA is discussed as well. The latter has to be regarded as an equivalent material selection with respect to some aspects, however, this publication points out that compared to polycarbonate PMMA would have a much greater tendency to form blisters when irradiated by means of a laser, as a result of which the process control would be much more complicated in order to avoid such bubbles in the case of PMMA. The absorption behavior of PMMA would also be disadvantageous.
DE 10 2013 100 888 A1 finally discloses a light concentrator or light distributor which is composed of a plurality of light guiding cells which are lined up in a transparent light guide body. The light guide cells are formed by interfaces which can be produced inter alia by means of laser radiation in the light guide body. In this connection, there is also a local change in the refractive index. However, the light distributor known from this document is only suitable for a perpendicular coupling. The light guide body and/or the substrate material are in most cases an inorganic material and/or a glass, and there is only a general reference to plastic materials and the fundamental suitability thereof.